644 ALTERATION OF FOEM BY GALL-PRODUCING INSECTS. 



inflated, enlarged, and sometimes fleshy. The whole gall resembles a bud or small 

 bulb; it is not unlike one of those bulbils which so often arise instead of flowers 

 on the flowering axis of certain species of Allium. They occur especially on the 

 Bird's-foot Trefoil {Lotus corniculatus), where they are produced by the gall-gnat 

 Gecidomyia Loti, on the various species of Mullein (Verbascwm Austriacum 

 nigrum, Lychnitis, &c.) by Gecidomyia Verbasci, on several species of Germander 

 {Teucriumj montanum, Scordium, &c.), caused by Lactomelopus Teucrii, and on 

 the Eampion {Phyteuma orbiculare), where they are produced by Gecidomyia 

 phyteum.atis. 



Closely allied to these bud-galls are those remarkable gall-structures which are 

 commonly known in Austria as "cuckoo-buds". The cuckoo is supposed to be 

 concerned in their formation, just as it is in that of the frothy saliva-like masses 

 deposited by the Gicada on the Cuckoo-flower {Gardam,ine pratensis). The name 

 " cuckoo-galls " may be employed for the whole of this sub-group. They are char- 

 acterized by their pale whitish colour, soft spongy tissue, and especially by the fact 

 that they only involve the base of the shoot, while the upper end can continue its 

 growth unaltered. In this respect they may be compared to a Pine-apple fruit, 

 where the axis rises above the fleshy collective fruit (cf. p. 436) as a green leafy 

 tuft, which does not lose its growing power even with the ripening of the fruit. 

 The history of the development of cuckoo-galls is probably like that of covering 

 galls; and the main distinction lies in the fact that in the former the gall is pro- 

 duced not merely from a single organ or some part of it, but from a whole group of 

 adjoining plant-members. The best known and most widely distributed gall of this 

 group is produced by the pine-apple aphis Ghermes abietis on the twigs of the Spruce 

 Fir (Abies excelsa, see fig. 362^, p. 634). Early in the spring, before the foliage-leaves 

 have begun to unfold, the parthenogenetic females, the foundresses of the colony, 

 attach themselves each to the base of a young leaf and lay a mass of eggs at the 

 spot to which they have adhered. The larvee, hatching, penetrate the surrounding 

 parts of the shoot with their beaks; the shoot swells, as do the bases of the 

 needles, and a growth, the Spruce gall or Pine-apple gall results. The gall somewhat 

 resembles a small Fir-cone about an inch long, with the surface divided into small 

 convex areas, each bearing a short needle-like projection in the middle; these are 

 the deformed needles, which, becoming swollen, touch each other on the outside of 

 the gall. They are separate inside, so that the gall contains a series of cavities or 

 chambers. In these chambers the larvae live in numbers, either entering the 

 chambers during the growth of the gall or being inclosed by the swelling of the 

 surrounding needles — this point is not certainly determined. They remain in the 

 small cavities so formed and feed, cast their skins, and multiply there. In August 

 the gall begins to dry up, each of the small cavities opens by a slit in front of the 

 green needle-point surmounting the cushion (see fig. 362 \ p. 534), and the winged 

 insects now leave the place in which they have passed the spring and summer. 



Cuckoo-galls are met with almost as frequently on Stellatse, viz. on various 

 species of Bedstraw (Galium Austriacum,, boreale, uliginosum,, &c.) and Woodrun 



